Hyperthreading
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We have just installed a Dell 1750 with duel Xeon 3.0, with 4G of memory, running SQL 2000 standard, with Windows Server 2003 enterprise. There is quite a lot of debate on whether hyperthreading should be turned on or off. With it turned on, the server appears to have 4 processors. Any experience on whether to leave HT on or off?
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We run it on here, but haven't really tested it turned off. Haven't had any issues though.
Steve Jones
http://www.sqlservercentral.com/columnists/sjones
The Best of SQL Server Central.com 2002 - http://www.sqlservercentral.com/bestof/
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hyperthreading works fine with sql server .. used dual zeon 4's on dell servers with sql std no probs .. shows significant performance gains .. never though about turning it off
[font="Comic Sans MS"]The GrumpyOldDBA[/font]
www.grumpyolddba.co.uk
http://sqlblogcasts.com/blogs/grumpyolddba/ -
We did some testing quite a while back, I think it was a pre production compaq with HT. It did work well, don't expect 2 to one, of even to match a true Multi. But you will see a boost when they can be used.
I've done some play with my DB server at home. Recently upgrade to HT, figure maybe 150% over a single. Nothing extremely formal, just ran a bunch of queries with it on and with it off.
But I haven't seen any isue's either.
KlK, MCSE
KlK -
What is hyperthreading and how to turn it on or off?
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Hyperthreading is funtionality with Intel CPUs that allows multiple threads to run concurrently on the same CPU. It apparently (I discovered recently) has existed in the pentium 3s but not implemented. Mostly Pentium 4s handle best and I think requires an 800Mhz front side bus to acctually be turned on. On those machines it is on by default or may require setting on in the BIOS. Once done you cannot go back without reisntalling the OS as it causes the OS to install the multi-processor kernel but cannot go the other way (should be fine to do on a multi processor system but I don't have one to test just a single to HT and off).
Note: I have heard some mumbles of issues related to parallel processing but have not experience or seen any documentation on this.
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The newer intel chips, support HT or hyperthreading technology. Which basically puts 2 processors on a single piece of silicon. It's not a true dual, they share cache and a number of functions, but there are dual instruction pipelines and 2 core processors. It allows a significant amount of internal processing to occur simultanously.
It must be an HT chip, and you usually turn it on via the BIOS. Windows must also be setup to handle multiple processors. If you have a single with HT it looks like 2, a dual with HT looks like 4, etc.
On a side note, there was the utility unitomp (???) to upgrade NT4. When I set up Win2003 I ended up reinstalling the OS to get it to recognize both. Does anyone know of a smiliar utility to upgrade Win2003 ??
KlK, MCSE
KlK -
We too just got some new HP's with the hyperthreading for our workstations. We have seen some funny screen refreshes with Office XP and 97 and Windows XP Pro. We have two machines that crash constatnly but all the ohter 12 seem to be working fine.
Next week, we will be installing SQL Standard on one for our internal development purposes. Hopefully it won't cause too many problems.
SJ
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HT is actually not two processor cores on one silicon die (like the processors we'll see in year or two). It's about maximizing usage of existing execution units (ALU, FPU, ..).
For some good (not dB related:) intro, look at: http://arstechnica.com/paedia/h/hyperthreading/hyperthreading-1.html
pedro
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How do we know if the HT is turned on from within the OS ? Is there any settings to tell or we need to reboot to get into BIOS to determine ? Thanks.
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Compare the number of physical processors in the server versus the number the OS sees. If the number is the same, no hyperthreading. If the number is 2x, hyperthreading.
K. Brian Kelley, GSEC
http://www.truthsolutions.com/
Author: Start to Finish Guide to SQL Server Performance Monitoring
K. Brian Kelley
@kbriankelley -
quote:
On a side note, there was the utility unitomp (???) to upgrade NT4. When I set up Win2003 I ended up reinstalling the OS to get it to recognize both. Does anyone know of a smiliar utility to upgrade Win2003 ??KlK, MCSE
There is no such utility for Windows 2003 because Plug and Play detects the correct kernel to use and changes it if necessary. If this did not happen with your server, you should contact the hardware vendor for the correct HAL code.
--Jonathan
--Jonathan -
First Pedro that was a great link on HT, so it basically allows the processor to be more efficient. Somewhat like multiprocessing allows the machine to use more processor, HT allows the processor to have less wait time.
Jonathan, my Win2003 machine did NOT detect the MP automatically. I had to reload the OS to get it to recognize the HT MP setup. I didn't try much, but did reboot many times before I gave up and reloaded, it's just a test box, so no big deal.
Finally, HT must be enabled in the BIOS, at least on my MB some may just turn it on if it detects a HT chip I don't know. Then per Jonathan the OS should auto detect it, but as I mentioned, it didn't on my machine.
If you open up task manager, and look in performance it will show a graph for each logical processor, you can look in SQL EM and under processors it should show one for each logical (and / or physical) processor.
KlK
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